<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

</body>
<script>
    var obj = {
        a:"a",
        b:'b'
    };
    Object.seal(obj);

    delete  obj.a;
    obj.c="c";
    obj.a="aa";
    console.log(obj);
</script>
</html>